One of the many mutated inhabitants living in the area of New Guinea under the atomic dust cloud, the Mutant Leeches are particularly lethal, able to slowly cause insanity in their prey before eventual death. Their origin isn't entirely known, although it's projected by Ryougen Nishiyama that the creatures likely fed on the polluted marsh which caused its mutation. The leeches were fond of climbing nearby trees and falling down in groups on top of their prey when they attacked.